This invention relates to carburetors for supplying a combustible fuel/air mixture to internal combustion engines and more specifically to a primer mechanism for such carburetors. Even more specifically, the present invention relates to a manually operable primer for supplying an initial charge of fuel to an engine to aid in starting the engine.
In small internal combustion engines, particularly those engines which are started by hand cranking, it is frequently desirable to provide a priming arrangement for introducing a fuel charge into the engine intake system to aid in starting the engine. Such priming arrangements are particularly desirable for internal combustion engines which are used in snow throwers, lawn mowers, and the like. Numerous priming systems have been marketed or have been illustrated in the patent literature.
Known priming arrangements are typically in the form of an operator actuated priming bulb which, when depressed, displaces a volume of air into a carburetor float bowl or fuel well to displace fuel from the carburetor float bowl or fuel well into the engine intake system. Such arrangements are illustrated, for example, in U.S. Pat. Nos. 4,203,405, and 4,404,933. U.S. Pat. No. 4,203,405 discloses a well priming arrangement wherein fuel is displaced from the well of the carburetor. U.S. Pat. No. 4,404,933 discloses a float bowl priming arrangement for displacing fuel from the fuel bowl. Priming bulbs with protruding nipples have been used in conjunction with diaphragm carburetors.
A problem with well priming systems is that, after a priming operation, fuel is only slowly replaced in the well. Therefore, if the operator attempts to prime the engine in rapid succession, no fuel is present in the well after the first priming operation so that the only effective priming operation is the first priming operation. Furthermore, each prime is limited to the volume of the well, which is quite small compared to the bowl. In the present invention, which is a bowl priming system, since the primer bulb is external to the carburetor, it can have a large volume thereby permitting concomitantly large primes with each depression. Since bowl priming systems are not susceptible to this problem, it is desired to provide a bowl type of priming system.
Prior art priming arrangements have been provided which are internally vented whereby the displaced air is replaced with air drawn from the interior of the engine. A disadvantage of internally and externally vented priming arrangements is that part of the displaced air is lost through the vent passage rather than performing useful work in displacing fuel from the bowl or the well into the carburetor throat and thereby reducing the effectiveness of the priming arrangement. Another problem with internally vented primer systems has been that calibration of the carburetor has been difficult to achieve due to bowl vacuum because of the small bowl vent.
Externally vented priming arrangements have also been provided in the prior art. However, a disadvantage of these externally vented priming arrangements has been that contaminant dirt and water particles in the ambient air which are drawn into the priming chamber have tended to contaminate the external vent aperture and the air passages, thereby clogging the aperture and preventing or hindering the priming ability of the arrangement. This also causes gravity feed of fuel through the carburetor.
It is, therefore, desired to provide a priming arrangement for an internal combustion engine wherein the vent aperture and air passages are not subject to contamination by water or dirt so that the priming mechanism will remain effective throughout the life of the engine.